From 3ff15b95b67d6d3758ba546ce39cb144a322d834 Mon Sep 17 00:00:00 2001
From: John Siirola <jsiirola@users.noreply.github.com>
Date: Tue, 30 May 2023 13:17:01 -0600
Subject: [PATCH] LP/QP repn: ensure that {}**0 is compiled to the constant 1

---
 pyomo/repn/linear.py            |  2 ++
 pyomo/repn/tests/test_linear.py | 12 ++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/pyomo/repn/linear.py b/pyomo/repn/linear.py
index 8945199b268..72c183f5a00 100644
--- a/pyomo/repn/linear.py
+++ b/pyomo/repn/linear.py
@@ -344,6 +344,8 @@ def _handle_pow_ANY_constant(visitor, node, arg1, arg2):
                 visitor, None, ans, (_type, _arg.duplicate())
             )
         return ans
+    elif exp == 0:
+        return _CONSTANT, 1
     else:
         return _handle_pow_nonlinear(visitor, node, arg1, arg2)
 
diff --git a/pyomo/repn/tests/test_linear.py b/pyomo/repn/tests/test_linear.py
index 0b0e2e8b68e..acc6d315251 100644
--- a/pyomo/repn/tests/test_linear.py
+++ b/pyomo/repn/tests/test_linear.py
@@ -852,6 +852,18 @@ def test_pow_expr(self):
         self.assertEqual(repn.linear, {id(m.x): 1})
         self.assertEqual(repn.nonlinear, None)
 
+        m.p = 0
+
+        cfg = VisitorConfig()
+        repn = LinearRepnVisitor(*cfg).walk_expression(e)
+        self.assertEqual(cfg.subexpr, {})
+        self.assertEqual(cfg.var_map, {id(m.x): m.x})
+        self.assertEqual(cfg.var_order, {id(m.x): 0})
+        self.assertEqual(repn.multiplier, 1)
+        self.assertEqual(repn.constant, 1)
+        self.assertEqual(repn.linear, {})
+        self.assertEqual(repn.nonlinear, None)
+
         m.p = 2
 
         cfg = VisitorConfig()